Zooplankton Biovolume Research Articles

Combining in situ and ex situ plankton image data to reconstruct zooplankton (>1 mm) volume and mass distribution in the global ocean

Abstract Plankton size spectra are important indicators of the ecosystem state, yet such measurements are typically biased by the available sampling methods. Here, we combined individual size measurement from two zooplankton imaging approaches—in situ observation by the Underwater Vision Profiler5 and Multinet-collection supplemented by ex situ imaging via Zooscan—obtained in the global ocean, to calculate zooplankton normalized biovolume size spectra (NBSS) for all organisms larger than 1 mm. The reconstructed NBSS combining both datasets resulted in increased biomass estimates by adding organisms poorly sampled by either of the methods. The optimal values measured by both methods are used to reconstruct the zooplankton biovolume and biomass distributions. The reconstructed slopes appeared steeper and closer to those measured only by the UVP5 (+7.6%) and flatter than those obtained only from the Multinet (−20%), particularly in tropical and temperate latitudes. The main difference in tropical and temperate NBSS from the two devices is due to the fragile rhizarians that were not accounted for when using net data. When possible, we suggest using in situ and ex situ technologies together, and we provide potential indications on how to correct for missing components of the community when only one method is available.

Seasonal variability drives differences in the structure of the calanoid copepod community in two contrasting regions of the Gulf of Mexico

Abstract Calanoid copepods (CC) are key contributors to the biological carbon pump and pelagic trophic dynamics. The deep-water regions of Perdido and the Bay of Campeche in the western and southern Gulf of Mexico (GM), respectively, differ in hydrography and productivity, leading to potential differences in copepod biomass and community structure. Zooplankton (0-200 m) were collected from the shelf edge to the deep-water region during the winter and summer autumn 2016. Calanoids contributed 38-60% of total zooplankton biomass and 55-70% of overall copepod abundance. The Bay of Campeche had the highest total zooplankton biovolume (287±120 ml 1000 m−3) and total mean copepod abundance (CC and non-calanoids ~146,000 ind. 1000 m−3) during summer-autumn, likely resulting from cross-shelf nutrient transport fueling local productivity. Adult females dominated calanoid numerical abundance (43-50%), thus suggesting a high reproductive potential. Cluster analysis showed differences between seasons (~40% dissimilarity) but not regions. Environmental conditions explained 22% of the variability in community composition; the winter assemblage was significantly related to oxygen concentrations, whereas the summer-autumn community was related to warmer conditions and higher integrated chlorophyll-a concentrations. The CC community responded to seasonal changes more than regionally related hydrographic differences, with likely implications for organic matter cycling and export.

Plankton diversity and dynamics in the upper surface of the Indian sector of the Southern Ocean ecosystem and biogeochemical processes

In the Southern Ocean (SO) marine ecosystem, the interplay between CO2 sink and climate change is closely linked to the shifting plankton communities, leading to potentially wide-ranging biogeochemical effects. Within the Indian sector of the Southern Ocean (ISSO), the phytoplankton community was predominantly composed of Fragilariopsis spp., followed by Chaetoceros sp., while the zooplankton consisted mainly of Pleuromamma spp. and Oithona similis. Plankton diversity is collectively influenced by variables such as temperature, photosynthetically available radiation (PAR), and macronutrient availability. During the austral summer of 2019, significant latitudinal variations in phytoplankton were observed at major fronts in the region, including the Subtropical Front (STF), Sub Antarctic Front (SAF), Polar Front (PF), and South of Polar Front (SPF). At the STF, flagellates dominated (87%), while their presence decreased to 12% at the SPF, while diatoms progressively increased from the STF (<1%) to the SPF (87%) through the SAF and PF. Chlorophyll a (Chl-a) concentrations at the surface were highest in the PF (0.62 mg m−3), followed by the SPF (0.56 mg m−3), SAF (0.51 mg m−3), and STF (0.28 mg m−3). The integrated Chl-a values across the water column were higher at the SPF (21.49 mg m−2) than at the STF (14.73 mg m−2). The dominant diatom species at the surface along the fronts, except for STF, was Fragilariopsis spp. (∼5 × 105 Cells L−1), followed by Chaetoceros sp. (∼1 × 105 Cells L−1), and Coscinodiscus sp. (∼5 × 104 Cells L−1). Conversely, at the STF, the most abundant flagellate species were Gyrodinium spp. (∼2.4 × 104 Cells L−1), followed by Protoperidinium sp. (∼2 × 104 Cells L−1), and Amphidinium sp. (∼1 × 104 Cells L−1). Zooplankton biovolume in the upper 200 m ranged from 0.71 to 10 ml 100 m−3, with relatively higher biovolume and numerical abundance found in the SAF compared to the PF. The higher Chl-a concentration in the PF and lower zooplankton biovolume could have significant negative consequences for higher trophic levels. PAR showed higher values up to 40 m than observed depths along the fronts. Additionally, variations in salinity and temperature were recorded, with a significant decline in temperature from the STF to the SPF. Nitrate (NO3−), phosphate (PO43−), and silicate (SiO44−) concentrations were higher at the SPF than at lower latitudes. Overall, these findings indicate that the plankton community composition in the study region is influenced by a diverse set of governing variables over time, highlighting the significant implications for the regional biogeochemical cycle.

Role of salinity on zooplankton assemblages in the tropical Indian estuaries during post monsoon

The estuary is the transition zone between the riverine and marine environments, in which the zooplankton act as a trophic connector in the energy transfers from primary producers to secondary consumers. Zooplankton biovolume and species assemblages with reference to physical, chemical and biological properties in the Indian estuaries are rarely studied. To examine the zooplankton variability in abundance and diversity, we therefore, investigated seventeen Indian estuaries during the post monsoon of the year 2012. Based on salinity conditions, estuaries were classified into oligohaline, mesohaline and polyhaline. A marked spatial gradient in salinity was observed between the upstream and downstream estuaries. Relatively, salinity was high in downstream areas, resulting in high zooplankton biovolume and diversity perceived in downstream areas. In contrast, nutrient concentrations were higher in the upstream than the downstream estuaries, resulting in high phytoplankton biomass (in terms of chlorophyll-a) perceived in the upstream estuaries. Zooplankton abundance was numerically dominated by Copepoda, constituting approximately 76 % of the total zooplankton count. Zooplankton population was highly similar between upstream and downstream in the oligohaline estuaries. In contrast, heterogeneous assemblages were noticed between upstream and downstream in the mesohaline and polyhaline estuaries. Under oligohaline conditions, surface waters dominated by Acartia clausi, A. dane, A. plumosa, Cyclopina longicornis, Oithona rigida and Tigriopus sp. In contrast, under mesohaline and polyhaline conditions, Acartia tonsa, Acartia southwelli, Acartia spinicauda, Paracalanus spp. Centropages typicus, Temora turbinate, Oithona spinirostris and O. brevicornis become the key dominant species. Eucalanus spp., and Corycaeus spp. were indicator species in the downstream estuaries. Our findings suggest that zooplankton diversity and numerical abundance were chiefly governed by salinity rather than phytoplankton biomass (chlorophyll-a) in the Indian estuaries during the post monsoon.

The Effect of Fish Production and Environmental Factors on Phytoplankton in Hypertrophic Fishponds

Fishponds form substantial part of standing water ecosystems in the landscape of the Central Europe. We studied the effects of fish production and environmental parameters on phytoplankton in fifteen fishponds of various size, fish production and situated at different altitudes. Water and plankton samples were collected from April to October 2018 and 2019. Phytoplankton abundance, zooplankton biovolume, total phosphorus, total nitrogen, ammonia-nitrogen, nitrites, nitrates, phosphates, and total iron concentration were determined. Based on average values of total nitrogen (8.53 mg.l-1), total phosphorus (0.399 mg.l-1), and chl-a (180 &micro;g.l-1) all fishponds were classified as hypertrophic. Fish production was significantly correlated only with altitude. With increasing altitude, fishponds have a lower nutrient content, lower temperature, and hence lower production. The direct effect of fish production on phytoplankton was not observed. Two environmental parameters significantly explained the variability in phytoplankton - altitude and total iron concentration. Our results indicate that besides traditionally monitored parameters like nitrogen and phosphorus concentration, the attention should also be focused on other factors potentially affecting studied ecosystems, hypertrophic fishponds.

Community structure and biomass of larval euphausiids and postlarval mysids in relation to anomalous warming events during a weekly time series (2014–2017) at Cabo Pulmo National Park, Mexico

Euphausiids and mysids are important components of pelagic ecosystems due to their high abundance and tendency to form dense aggregations, swarms, and schools, which concentrate biomass that attracts visual predators. Species richness, abundance, and carbon biomass of euphausiids and mysids were investigated from a weekly daytime surface zooplankton time series from 2014 to 2017, in relation to 15 environmental variables at Cabo Pulmo National Park (CPNP, 23°27′ N, 109°25′ W), Mexico. A marine heatwave (MHW; January–August 2014) and El Niño 2015–2016 (May 2015–May 2016) caused anomalously warm temperatures in relation to the 2002–2018 temperature time series. We tested the hypotheses that CPNP is dominated by a tropical euphausiid and mysid species assemblage and that abundance of both taxonomic groups decreased during the MHW 2014 and El Niño 2015–2016. Euphausiids (7.9 ind. m−3) had a higher mean abundance than mysids (3.4 ind. m−3). Eight euphausiid species, mostly of tropical-oceanic affinity, were collected (98 % larvae). Nyctiphanes simplex decreased and Euphausia distinguenda and Stylocheiron carinatum increased in abundance during El Niño 2015–2016. Five mysid species were collected (juveniles and adults). Mysidium rickettsi alone accounted for 99.98 % of total mysid abundance. Although the euphausiids collected were mainly larval stages, due to sampling in shallow coastal waters during the day, they contributed more biomass than juvenile and adult M. rickettsi in the pelagic habitat, though the abundance of this mysid in its epibenthonic habitat was likely underestimated. A canonical correspondence analysis of euphausiid and mysid abundance as a function of 10 environmental variables explained 77.4 % of the total variability, showing greater seasonal (warm vs cold) than interannual changes. The best correlated environmental variables with euphausiid and M. rickettsi abundance were net primary production (−0.419), zooplankton biovolume (0.3177) and the MEI.v2 (−0.278). We concluded that the most evident changes in community structure and abundance were seasonal (e.g. N. simplex dominated during the cold season while E. distinguenda dominated during the warm season) rather than interannual. Moreover, the abundance and biomass of euphausiids decreased during the MHW 2014 and El Niño 2015–2016; paradoxically the highest abundance and biomass of E. distinguenda and the mysid M. rickettsi occurred during El Niño 2015–2016. This implies higher available biomass for benthonic and nektonic predators in this neritic tropical reef ecosystem, contrasting with decreased abundance of euphausiids observed along the west coast of the Baja California Peninsula during this period.

Hydrodynamics and zooplankton assemblages in Prydz Bay, East Antarctica, during the austral summer of 2017

Vertical distribution of zooplankton biovolume, abundance and community composition in the twilight zone are important to better understand their role in carbon and energy transfer that mediate the food web structure in the Prydz Bay. Qualitative and quantitative zooplankton studies were carried out in January 2017, using a multi plankton sampler (mouth area: 0.25 m2; 200-microns mesh size) in the ice-free domain of the Prydz Bay. In this study, we investigated the diel variation of zooplankton biovolume and community structure between the surface water layer and 500 m depth at every six hours intervals for a period of 48 h at about 68° S latitude, 74° E longitude in the Prydz Bay. Besides, relationship between the zooplankton assemblages and diffrent water masses were also discussed. We found an abrupt increase in zooplankton biovolume within the mixed layer depth on day 1 (13:15 h). Apart from high, localized contributions from chaetognaths, appendicularians and polychaete larvae, mesozooplankton was numerically dominated by copepods, and densities were highest near the surface most of the times. Two water masses were identified based on the signatures of temperature and salinity: Antarctic Surface Water (ASW) and Shelf Water (SW). ASW had a higher proportion of Calanoides acutus, Calanus propinquus and Oithona similis, while Metridia gerlachei, and Heterorhabdus austrinus were mostly encountered in SW. Our results will help to predict the short term temporal variations of copepods assemblages and other zooplanktons according to the dynamics of hydrographic features in Prydz Bay.

Characterization of hydrological features and plankton during neap tides in a subtropical lagoon south of the California Current

ABSTRACT This study aimed to characterize their Spatio-temporal distribution of hydrological variables and plankton during neap tides in Bahía Magdalena, a subtropical lagoon south of the California Current. We compare data from surface and bottom waters of stations located inside the lagoon with those near the bay's mouth and between surface and bottom. The availability of nutrients and the chlorophyll-a are associated primarily with the intense upwelling activity in spring. Due to direct marine influence, this relationship was more significant at the inlet than inside the lagoon, especially at the bottom. During the intense upwellings marine influence is maintained even during neap tides. The wind probably causes the homogeneous distribution in most variables within the bay's surface; this may also contribute to the re-suspension of nutrients due to vertical water column mixing. Abiotic variables were not linearly related with zooplankton biovolume and the density of diatoms and dinoflagellates. Phytoplankton was composed mainly by the micro fraction and diatoms during spring and nanoplankton in the warmest season of the year; however, the strong upwellings at the spring's end caused a HAB composed for diatoms. Chlorophyll-a concentration and diatoms were more abundant inside the lagoon and could explain the lower nutrient concentration of that zone. Zooplankton biovolume seasonality differed from other years, with higher values during winter and a significant decreasing trend throughout the year, resulting from the phytoplankton variability. Upwelling and wind variability explains the high biological productivity observed over most of the year.

Magnitude of river discharge determines the food habit and community composition of zooplankton in the Indian estuaries during monsoon

Zooplankton of seventeen Indian estuaries were investigated using plankton net (200-μM mesh; 0.25 m2 mouth area) during the peak discharge period of 2011. Results showed that the seventeen estuaries are comparable in terms of area, and volume of river runoff. Indian estuaries differ by their level of river runoff (highest in the Godavari), suspended matter concentration (highest in the Haldia), and potential phytoplankton biomass (Chlorophyll-a) (highest in the Kaveri). Relatively higher zooplankton biovolume was observed in the estuaries which receive low discharge, than in estuaries with high discharge. Zooplankton abundance was numerically dominated by calanoids, constituting approximately 69% of the total zooplankton count. Community composition in the Northern Indian Estuaries (NIE) was dominated by Acartiella spp., and Diaptomus spp. On the other hand, taxa such as Acartia spp., Acrocalanus sp., and Paracalanus spp. were predominant in the Southern Indian Estuaries (SIE). Zooplankton community structure was driven by terrestrial organic carbon and river discharge in the NIE. Whereas both salinity and phytoplankton biomass (Chl-a) played a crucial role in the SIE. Therefore, this study suggests that Indian estuaries were driven by the magnitude of river discharge, resulting in variations in hydrological, chemical, and biological properties, which in turn amends the zooplankton community composition and food habits.

Cephalopod paralarval species richness, abundance and size structure during the 2014–2017 anomalous warm period in the southern Gulf of California

AbstractCephalopod paralarval species richness, abundance and size structure were surveyed wduring an anomalous warm period (2014–2017) in the Cabo Pulmo National Park (CPNP), Gulf of California, Mexico. Paralarval taxa from six families (Cranchiidae, Enoploteuthidae, Ommastrephidae, Onychoteuthidae, Argonautidae and Octopodidae) were identified. Most taxa were of tropical biogeographic affinity and oceanic habitats. Highest paralarval richness occurred during spring associated with the northward movement of Tropical Surface Water, while the lowest was recorded during autumn with the southward flow of the Gulf of California water mass. Although 89% of the paralarvae were collected at or close to their species hatching size, none of the paralarval taxa showed a consistent seasonal spawning period. A canonical correspondence analysis showed three taxonomic assemblages: Argonauta and Helicocranchia–Onychoteuthis groups correlated with northward currents and high zooplankton biovolumes (ZB) and SD complex–Abraliopsis group with southward currents and intermediate ZB. Our Helicocranchia pfefferi paralarvae are the first recorded for the Gulf of California. At least 11 cephalopod taxa reproduce in CPNP. This area represents a suitable spawning habitat for cephalopods of socio-economic value.

Linking mangroves and fish catch: a correlational study in the southern Caribbean Sea (Colombia)

Mangroves provide habitat to a variety of fish species, potentially enhancing fish production in small-scale fisheries. Fish production ecosystem services have been correlated with mangrove area and perimeter in many tropical locations; however, nothing has been published linking small-scale fish catch and mangrove attributes in the southern Caribbean Sea. We correlated environmental variables with experimentally-derived catch per unit effort (CPUE) and richness of fishes in the Colombian southern Caribbean Sea, an area not directly connected with other productive coastal habitats. Concurrently, we measured mangrove attributes (area, perimeter, above-ground carbon), water quality (salinity, total dissolved solids), and water column productivity parameters (chlorophyll a, seston, zooplankton biovolume). Mangrove area and zooplankton biovolume were the main factors influencing fish species richness. Mangrove area was positively correlated with catches for three of the most common fish species in the local artisanal fishery: Ariopsis canteri Acero P, Betancur-R, and Marceniuk, 2017, Mugil incilis Hancock, 1830, and Sciades proops (Valenciennes, 1840), which represent about 22% of the total regional annual catch. Our results suggest causal links between mangrove habitat and fishery production through a mangrove trophic contribution. Ariopsis canteri appears to be a mangrove-dependent species and M. incilis a mangrove- associated species. These results support managing or preserving mangroves in the most extensive areas in the southern Caribbean to sustain small-scale fishery resources used mainly for community sustenance where alternative resources are limited.

Spatio-temporal trends in zooplankton biomass in the northern Humboldt current system off Peru from 1961-2012

Anchovy (Engraulis ringens) is the most important exploited fish species in the Northern Humboldt Current System (NHCS) off Peru. This species, as well as most other pelagic resources, mainly forage on zooplankton. The NHCS is bottom-up controlled at a variety of scales. Therefore, fish biomass is driven by the abundance of their prey. In this context, we studied the spatiotemporal patterns of zooplankton biomass in the NHCS from 1961-2012. Data were collected with Hensen net all along the Peruvian coast. To transform zooplankton biovolume into biomass we used a regression that was calibrated from 145 zooplankton samples collected during four surveys and, for which, precise information was available on both biovolume and wet weight. The regression model was then applied on a time-series encompassing 158 cruises performed by the Peruvian Institute of the Sea (IMARPE) between 1961 and 2012. We observed a clear multidecadal pattern and two regime shifts, in 1973 and 1992. Maximum biomass occurred between 1961 and 1973 (61.5 g m−2). The lowest biomass (17.8 g m−2) occurred between 1974 and 1992. Finally, the biomass increased after 1993 (26.6 g m−2) but without reaching the levels observed before 1973. A seasonal pattern was observed with significantly more biomass in spring than in other seasons. Spatially, zooplankton biomass was higher offshore and in northern and southern Peru. Interestingly, the zooplankton sampling was performed using classic zooplankton net that are well fitted to mesozooplankton and are known to underestimate the macrozooplankton; however, the spatiotemporal patterns we observed are consistent with those of macrozooplankton, in particular euphausiids. This suggests that in the NHCS, when and where macrozooplankton dominates it also dominates the biomass obtained using classic zooplankton net samples. Finally, until now, in the NHCS only time-series on zooplankton biovolume were available. The biomass data we provide are more directly usable in trophic or end-to-end models.

The relationship between zooplankton distribution and hydrography in oceanic waters of the Southern Gulf of Mexico

Zooplankton was sampled in the Southern Gulf of Mexico, during autumn 2010, summer 2011 and winter 2013. Hydrographic data, dynamic topography and geostrophic velocities showed the presence of alternating cyclonic and anticyclonic gyres in the area, and a quasi-permanent gyre in the Bay of Campeche, with higher surface temperatures and lower salinities during autumn and summer, than in winter. Stronger rainfall was present during summer, which coincided with a strong salps “bloom” that considerably increased biovolumes. A significant difference in biovolumes was found for the three seasons, with highest zooplankton biovolumes during summer, and lowest during autumn. A shoaling of higher fluorescence and higher nutrients (Nitrate + Nitrite) was found in the BOC, in coincidence with higher biovolumes during the three seasons sampled. Multivariate analysis showed that the variables controlling the productivity were mainly fluorescence and nutrients for summer 2011 and winter 2013. Higher biovolumes were present in autumn, summer and winter at the same stations, being higher during summer. Data obtained show that the Bay of Campeche is a high productivity area, all year round, particularly inside the quasi-permanent gyre where high biovolumes were present in autumn, summer and winter, but with considerable seasonal variations in primary and secondary productivity, probably dependent in great measure from river discharge and rainfall.

The ‘suitcase hypothesis’: Can entrainment of meroplankton by eddies provide a pathway for gene flow between Madagascar and KwaZulu-Natal, South Africa?

Similarities in the marine fauna found off the coasts of southern Madagascar and KwaZulu-Natal Province (KZN), South Africa, led to the development of the ‘suitcase project,’ with the aim of establishing whether eddies that form off southern Madagascar may package and transport biological material across the Mozambique Channel, facilitating connectivity and gene flow. Meroplankton (larval stages of fishes and benthic invertebrates) were collected on the Madagascan shelf and along a transect through a cyclonic eddy in the Mozambique Channel. The samples were analysed using microscopy and DNA barcoding, seeking to identify species known to be common to both the southeast coast of Madagascar and the east coast of South Africa and thereby to reveal potential indicators of connectivity between these regions. The greatest zooplankton biovolume in the upper 200 m occurred on the shelf, followed by in the western part of the eddy and in the region outside the eddy to the west, and was lowest in the region outside the eddy to the east. The meroplankton were dominated by taxa of coastal origin and these were also most abundant on the shelf and in the western part of the eddy, with the lowest abundances in the region outside the eddy to the east. The findings show greater zooplankton biovolumes and larval abundances and the presence of reef-associated larval assemblages on the Madagascan shelf and along the transect through the cyclonic eddy, providing support for the suitcase hypothesis that planktonic organisms are entrained within eddies as they propagate south-westwards of the Madagascan shelf.

How Efficient Are Semi-Natural Ponds in Assimilating Wastewater Effluents? Application to Fuente de Piedra Ramsar, Mediterranean Salt Lake (South of Spain)

This work concerns the case study of a Mediterranean Ramsar salt lake (Fuente de Piedra, southern Spain) that receives the treated wastewater of the local village treatment plant. The wastewater goes through a system of canals, water dams, and three semi-natural ponds that were built in 2005. This work aims to investigate the capacity of the system to assimilate the impact of wastewater effluents on Lake Fuente de Piedra. For this, four points were sampled on 27–29 April 2016, at the inlet and the outlet points of the first and the third semi-natural ponds, with three replicates each. Temperature, pH, and conductivity at the inlet were 19.62 °C, 7.99, and 3262.67 μS/cm, respectively, and increased through the pond system by 7.59%, 8.04%, and 37.34%, respectively. Phytoplankton concentration indicators decreased from the inlet point to the outlet point (chlorophyll a from &gt;500 to &lt;20mg/L), as did the biovolume (from &gt;5 × 1010 to 4.3 × 109 μm3/mL). Zooplankton biovolume, in contrast, increased three orders of magnitude from the inlet (3.5 × 107 μm3/mL) to the outlet point (1.6 × 109 μm3/mL). Heterotrophic bacteria (1.29 × 105 cfu/mL) and faecal enterococci (1033 ± 351 cfu/100 mL) were high at the inlet point, but decreased at the outlet point by almost three orders of magnitude. Total phosphorous and total nitrogen decreased 40.3% and 23.1% through the pond system. The results showed an improvement in water quality in its passage through the built system. Additionally, as permanent wetlands with acceptable water quality, the water system attracts wild fauna during the dry summer, leading to the conclusion that these semi-natural or artificial wetlands should be extrapolated to other aquatic ecosystems (Mediterranean wetlands) that receive contributions of residual waters. Better functioning of the treatment plant is desirable to improve the conservation of the Ramsar and adjacent wetlands systems.

Effects of temperature increase on zooplankton size spectra in thermal discharge seawaters near a power plant, China

Utilizing the plankton 1 (505 Μm), 2 (160 Μm), 3 (77 Μm) nets to seasonally collect zooplankton samples at 10 stations and the corresponding abundance data was obtained. Based on individual zooplankton biovolume, size groups were classified to test the changes in spatiotemporal characteristics of both Sheldon and normalized biovolume size spectra in thermal discharge seawaters near the Guohua Power Plant, so as to explore the effects of temperature increase on zooplankton size spectra in the seawaters. The results showed that the individual biovolume of zooplankton ranged from 0.00012 to 127.0 mm3·ind-1, which could be divided into 21 size groups, and corresponding logarithmic ranges were from -13.06 to 6.99. According to Sheldon size spectra, the predominant species to form main peaks of the size spectrum in different months were Copepodite larvae, Centropages mcmurrichi, Calanus sinicus, fish larvae, Sagitta bedoti, Sagitta nagae and Pleurobrachia globosa, and minor peaks mostly consisted of individuals with smaller larvae, Cyclops and Paracalanus aculeatus. In different warming sections, Copepodite larvae, fish eggs and Cyclops were mostly unaffected by the temperature increase, while the macrozooplankton such as S. bedoti, S. nagae, P. globosa, C. sinicus and Beroe cucumis had an obvious tendency to avoid the outfall of the power plant. Based on the results of normalized size spectra, the intercepts from low to high occurred in November, February, May and August, respectively. At the same time, the minimum slope was found in February, and similarly bigger slopes were observed in May and August. These results indicated that the proportion of small zooplankton was highest in February, while the proportions of the meso- and macro-zooplankton were relatively high in May and August. Among different sections, the slope in the 0.2 km section was minimum, which increased with the increase of section distance to the outfall. The result obviously demonstrated that the closer the distance was from outfall of the power plant, the smaller the zooplankton became. On the whole, the average intercept of normalized size spectrum in Xiangshan Bay was 4.68, and the slope was -0.655.

Environmental quality and natural food performance at feeding sites in a carp (Cyprinus carpio) pond

Just like other domesticated animals, common carp (Cyprinus carpio) are able to learn where food can easily be obtained. As a result, carp in semi-intensive polyculture ponds could conceivably restrict their main activity centres to supplemental feeding sites, leading to lowered exploitation of natural food resources (zooplankton and macrozoobenthos) and localised degradation of environmental conditions. At two semi-intensive ponds in southern Moravia (Czech Republic), areas around feeding sites displayed significantly reduced oxygen concentration and saturation (mainly p < 0.001). Likewise, temperature, pH and transparency also decreased significantly at feeding sites (mainly p < 0.05), while turbidity increased. While there was no significant difference in zooplankton biovolume at feeding and non-feeding sites, zoobenthos density and biomass were significantly lower at feeding sites (mainly p < 0.01). The feeding behaviour of carp, therefore, led to significant changes in both abiotic and biotic conditions at supplemental feeding sites.

Measuring the distribution, abundance, and biovolume of zooplankton in an oligotrophic freshwater lake with a 710 kHz scientific echosounder

AbstractAcoustic surveys of the distribution and abundance of freshwater zooplankton were conducted in Lake Giles, an oligotrophic freshwater lake. Volume backscatter data from a 710 kHz scientific echosounder were converted to high‐resolution spatial and temporal numerical density estimates of small zooplankton. Vertical net tows of a 153 μm mesh closing bongo net at multiple depth intervals provided both identification of the types and sizes (0.5–1.5 mm length) of crustacean zooplankton present in the lake as well as an independent measurement of zooplankton numerical density. Net and acoustic estimates of zooplankton abundance, biovolume, and distribution were very similar. The improved resolution of the high‐frequency acoustic sampling provides insight into several aspects of freshwater zooplankton ecology including: separation of migrating and non‐migrating zooplankton, high resolution measurements of in situ zooplankton biovolume, calculation of in situ vertical velocities of migrating zooplankton, and fine‐scale (sub‐meter) horizontal and vertical zooplankton distribution during daytime, nighttime, and vertical migration events. These methods allow for more detailed and accurate estimates of zooplankton distribution than traditional net sampling methods can provide, including determining the total abundance of organisms within a specific habitat. They also provide higher resolution data in both space and time of smaller zooplankton taxa than have been measured previously in freshwater ecosystems.

Is the Russell Cycle a true cycle? Multidecadal zooplankton and climate trends in the western English Channel

The Russell Cycle is one of the classical examples of climate influence on biological oceanography, represented as shifts in the marine plankton over several decades with warm and cool conditions. While the time-series data associated with the phenomenon indicate cyclical patterns, the question remains whether or not the Russell Cycle should be considered a “true cycle”. Zooplankton time-series data from 1924 to 2011 from the western English Channel were analysed with principal component (PC), correlation and spectral analyses to determine the dominant trends, and cyclic frequencies of the Russell Cycle indicators in relation to long-term hydroclimatic indices. PC1 accounted for 37.4% of the variability in the zooplankton data with the main contributions from non-clupeid fish larvae, southwestern zooplankton, and overall zooplankton biovolume. For PC2 (14.6% of data variance), the dominant groups were northern fish larvae, non-sardine eggs, and southern fish larvae. Sardine eggs were the major contributors to PC3 (representing 12.1% of data variance). No significant correlations were observed between the above three components and climate indices: Atlantic Multidecadal Oscillation, North Atlantic Oscillation, and local seawater temperature. Significant 44- and 29-year frequencies were observed for PC3, but the physical mechanisms driving the cycles are unclear. Harmonic analysis did not reveal any significant frequencies in the physical variables or in PCs 1 and 2. To a large extent, this is due to the dominant cycles in all datasets generally being long term (>50 years or so) and not readily resolved in the examined time frame of 88 years, hence restricting the ability to draw firm conclusions on the multidecadal relationship between zooplankton community dynamics in the western English Channel and environmental indices. Thus, the zooplankton time-series often associated and represented as the Russell Cycle cannot be concluded as being truly cyclical.

Response of micro- and mesozooplankton in the southwestern Bay of Bengal to a cyclonic eddy during the winter monsoon, 2005.

A cyclonic eddy (CE) in the southwestern Bay of Bengal (SWBoB; 10-15° N; 81-87° E) during winter monsoon 2005 and associated changes in the open ocean hydrography and productivity patterns were studied using satellite observations and in situ measurements. Analysis of the satellite-derived sea surface height anomaly (SSHA) indicated the existence of a large eddy (10-15° N; 81-87° E) from November to January, with its core centered at 13° N and 82° E. The large positive wind stress curl (~1.8 × 10(-7) N m(-2)) and resultant Ekman pumping (~3 × 10(-2) cm s(-1)) were identified as the prominent forcing mechanisms. In addition, the cyclonic storms and depressions experienced in the region during the study period seem to have served to maintain the strength of the CE through associated Ekman pumping. The cold (~26.6 °C), nutrient-enriched (NO3 > 2 μM, PO4 > 0.73 μM and SiO4 > 3 μM) upwelled waters in the upper layers of the CE enhanced the biological production (chl. a > 0.56 mg m(-3)). Dissolved oxygen in the surface waters was > 200 μM. The phytoplankton and zooplankton biomass recorded during the season was comparable or perhaps higher than the peak values reported from the northeastern Arabian Sea (chlorophyll a concentrations of 0.2 to 0.4 mg m(-3) and zooplankton biovolume 0.6 ml m(-3)) during winter. Occurrence of a higher mesozooplankton biovolume (0.8 ml m(-3)) and relatively low abundance of microzooplankton indicates the prevalence of a short food chain. In conclusion, high biological production, both at primary as well as secondary level, suggests the prevalence of an efficient food web as a result of physical forcing and subsequent ecological interactions evident up to tertiary level in an oligotrophic basin like BoB.